Many portable devices, for example mobile telephones, contain a number of acoustic transducers, such as microphones, earpieces and speakers. Such transducers are key components in mobile phone audio/acoustic design. Generally, there will be one or more sound channels or back cavities associated with each acoustic transducer. Such sound channels can ensure a certain frequency response is obtained for the transducer, and must be carefully designed as part of the mechanical configuration of the device hardware. Small changes in the size and configuration of the sound channels or cavities can have a large effect on the acoustic properties of the combined transducer/sound channel.
In known acoustic transducer configurations, the mechanical design of the sound channels is fixed at the point of hardware design and manufacture of the device is completed, and cannot be later adapted during use for a specific purpose or desired configuration. Instead, the desired acoustic properties are produced by filtering the electrical signal representing the sound output before the signal is applied to the transducer. Typically, this requires the use of significant processing power, commonly provided by dedicated digital signal processors (DSPs).
Furthermore there is a limit to the modification of the acoustic response of the transducer which can be carried out in the DSP.
An example of the limitations of the mechanical design of typical microphone transducers is that of wind noise. Wind noise is a problem particularly for miniaturised designs such as found in mobile phone where there is no room for mechanical protection of the microphone from wind such as used in broadcast microphones like wind screens or foam protectors. Furthermore filtering out the wind noise from the signal in the electrical domain, not only requires significant processing power in a digital signal processor, but typically produces poor results as the sound pressure levels generated by the wind cause the microphone acoustic element to saturate.